After decades of ADHD intervention research, only two intervention approaches (i.e., psychopharmacology, behavioral treatment) have a "well-established" evidence-base supporting their efficacy for children with ADHD. Both of these interventions have inherent limitations. Recently multiple studies have demonstrated that cognitive training may improve neuropsychological and behavioral functioning in children with ADHD. The magnitude of treatment effects for cognitive training has been comparable to treatment effects for behavioral treatment for ADHD (i.e., small to moderate effect sizes). A limitation of existing cognitive training programs that may limit their efficacy is that each has employed a unifaceted approach. Each intervention program has targeted a single cognitive domain (e.g., working memory). This is problematic since as a group, children with ADHD have multiple areas of cognitive deficit (i.e., working memory, attention, response inhibition, delay aversion, intra-individual variability) and thus a unifaceted intervention does not address the multifaceted array of cognitive dysfunction in children with ADHD. Also, because individuals with ADHD each have unique patterns of cognitive deficits, a unifaceted cognitive training approach may target areas which are non-deficient and miss areas of significant deficit in individual patients depending on their ideographic cognitive profile. The primary goal of the proposed research is to develop and test a multifaceted cognitive training intervention that addresses a comprehensive array of ADHD- related cognitive deficits thereby ensuring that children's unique areas of cognitive deficit are targeted. During Phase I (R21 grant), software and a manual will be developed consisting of four training tasks targeting response inhibition, verbal working memory, attention, and delay aversion. Each task will possess advancing levels of difficulty. On each task, children will receive feedback on performance accuracy as well as on intra-individual variability in reaction times. The software will be pilot tested in Phase I to determine performance thresholds and intervention duration. Also, focus groups will be conducted to obtain patient perceptions of each task's difficulty and interest level. In Phase II (R33 grant), a preliminary randomized clinical trial will be conducted in order to obtain initial estimates of treatment efficacy. Pre-, post-, and follow up outcomes will be collected on a wide range of neuropsychological, behavioral, and academic measures. Effect size estimates across outcomes will be used to guide sample size determinations for future clinical trials of multifaceted cognitive training.